1. Field of the Invention
This invention relates to a developer container for replenishing an electrostatic copier or printer with a powder developer. More particularly, this invention relates to a developer container having a rotary or sliding valve provided at an outlet through which the developer is discharged.
2. Description of the Prior Art
Previously, valves for use in a developer container for replenishing an electrostatic-type copier or printer with powder developer have movable and fixed parts wherein moving (i.e., operating) the movable part of the valve device operates to open or close a discharge opening of the container. Packing is generally interposed between the movable and fixed parts in order to effect powder sealing such that when the discharge opening is closed, a compressive stress is applied to the packing. Conventionally, this packing is formed from an elastic material such as a rubber or rubber sponge, e.g., EPDM (a terpolymer elastomer made from ethylene-propylene diene monomer), chloroprene rubber, or urethane rubber, or from a foamed material made of polyethylene, polypropylene, polyurethane and the like.
Thus, the sealing properties of the valve device are produced and maintained by compressing the packing member and bringing the same into close contact with the mating member by virtue of an elasticity force thereby produced. However, since developer for processing in electrophotographic copiers or printers is a fine powder with a particle size of less than about 20 .mu.m with a fluidity-enhancing additive such as silica, a high degree of sealing performance is required. Thus, compressive stress may be increased so as to improve the sealing performance. In practice, however, increased compression makes it very difficult to smoothly open or close the valve because of an increase in the vertical reaction. If, conversely, the compressive stress is reduced, or if the packing is formed from a harder material so as to facilitate easier operation of the valve, sealing performance decreases. In this instance, even though the container is otherwise free from developer leaks under ordinary conditions, it nevertheless cannot remain completely sealed if it is dropped and receives an impact, or if it is used under severe conditions such as a low-temperature environment. In these events, it is necessary to utilize additional conventional sealing means such as fusing. However, it is not preferable to utilize fused containers for developer containment because once such developer container is opened, it is not possible to restore a requisite state of sealing thereto.